1. Field of Invention
This invention relates to a method and a form liner useful in the method for imparting an artistic surface relief pattern to a concrete wall.
2. Brief Statement of the Prior Art
Concrete wall construction is typically accomplished by a poured in place method in which vertical concrete containing forms are fabricated at the location for the wall, and the concrete is poured into the forms. The concrete hardens sufficiently to permit the forms to be removed within one day. A more popular method, particularly in southern climates of this country is the tilt-up method, in which concrete containing forms are fabricated on a horizontal floor, the concrete is poured into the form. After the concrete has hardened and cured for approximately a week, the forms are stripped and the walls are lifted, or tilted, into place. Typically, in this construction, the concrete foundation and floor for a building are constructed and the concrete retaining forms to construct the walls of the building are framed and on the floor. The aforementioned construction methods are used predominately for industrial buildings such as factories and warehouses. Concrete walls have been used to a limited extent for office building construction, however the starkness and unrelieved texture of most concrete walls has discouraged its wide application for office buildings.
Attempts have been made to impart an artistic relief to walls formed in this manner. One attempt which has been used in various applications has been lining of the concrete retaining forms with foamed plastic liners, rigid sheets of plastic foam which have one surface relieved with a negative impression of the desired relief in the concrete. These liners are placed on the floor of the building within the perimeter frame for the walls and concrete is poured into the perimeter frame for the walls and concrete is poured into the perimeter frame and over the foamed plastic form liners. After the concrete has cured and the walls are tilted into a vertical position, and the form liners are stripped from the wall leaving a surface relief texture or pattern on the exterior surface of the wall.
One technique for fabricating the plastic foam form liners has been machine or hand carving of the plastic foam. Various carving tools have been used such as a hot wire, knife, router and the like. The difficulty with this approach is that the carving of the form liners unavoidably forms a surface having a multiplicity of voids and broken plastic foam beads. The voids and broken beads capture the concrete and tenaciously adhere to the concrete after curing. As a consequence, it is difficult to strip the form liners from the concrete wall and the form liners must be demolished and residues of the liner must be washed from the wall with solvent. In my prior U.S. Pat. Nos. 3,515,779 and 3,702,180, I disclose and claim the use of molded plastic foam form liners. In this application, the foam liners are formed by the expansion of polystyrene beads in a conventional steam chest, against a metal mold that has a positive pattern of the desired relief. This method is superior to the aforementioned carving method for preparing the form liners since the surface of the form liners is smooth and the form liners do not adhere so tenaciously to the concrete wall. The disadvantages of this method, however, are that the liners must be fabricated with relatively expensive or sophisticated equipment using metal molds which are quite costly. Also, even though these liners do not adhere as tenaciously to the concrete wall as carved liners, their adhesion is sufficient to require that the molded foam liner be at least one inch in thickness to avoid excessive breakage or fragmentation of the liners when they are stripped from the concrete wall. This requirement that the liner be at least one inch in thickness increases the expense because of the substantial amount of material required and because it requires that the retaining wall for the concrete be built up with additional furring strips. Most tilt-up construction requires concrete walls seven inches in thickness. These walls are formed using retaining forms constructed with conventional dimensional lumber of 2 inches by 8 inches. This lumber is actually 7.5 inches in width, and there is only a tolerance of 0.5" in the height of the retaining form. The form is thus not sufficiently high to provide a concrete wall of a minimum of 7" in the thickness using the form liners. As a consequence, furring strips must be laid along the retaining forms to increase their height, a labor intensive requirement.